You're looking for High Tech and Industrial, but also important is high population and rich if possible. Those should give you the best selection. Like someone else said, if you look for systems exploited in Powerplay by Lui Yong Tui, you'll also get a discount, which reduces the buyback on your ship as an extra bonus.
Just so you're aware, the stock of modules in stations isn't static; it changes from time to time. There's speculation that there's a limited stock of each module and if enough people buy the same one, the stock runs out... so something you found in one place might not be there next time, though to be fair, it doesn't change that much.
Good choice on the Cobra. It's the fastest ship in the game (also the best in my opinion, but then I'm a Cobra pilot)
